I have, in the past, used both IVIG and plasmapheresis due to Sjogren's with neurological manifestations as well as antiphospholipid syndrome and can tell you IVIG (for neuropathy treatment) usually requires (due to cost) positive nerve tests/biopsy in order to be covered by insurance. I also can't imagine plasmapheresis (big guns) being used until they have determined the cause and/or at least documented something specific that would benefit from this.

As for Plaquenil, it is a DMARD (disease modifying anti-rheumatic drug) that is used for autoimmune diseases to help 'modify' the immune system and reduce symptoms. It typically helps with joint pain, fatigue and maybe some simple AI disease symptoms, but not neuropathy. It does take up to 6 months to begin working, but again don't get your hopes up for neuropathy relief.

Hopefully you'll do well with the cymbalta and lyrica. Pain mgmt can be a frustrating process, but I trust you'll find the right combination at some point.